1. Field of the Invention
The present invention relates to, a semiconductor laser device for use in an optical pickup and the like which optically reads information recorded in an optical recording medium such as an optical disc, and to an optical pickup using the semiconductor laser device.
2. Description of the Related Art
In the optical pickup which reads signals in optical discs such as CD-ROM and MD(Mini Disc), a semiconductor laser device is employed. The semiconductor laser device may be of (1) a type, mainly the CAN type, in which single pieces of semiconductor laser element, optical component and signal detecting element are discretely fabricated, or (2) a type called the hologram laser type in which a diffraction grating, a signal detecting element and a semiconductor laser element are integrally formed.
Among these types, a semiconductor laser device of the hologram laser type, described in (2) above, is so configured that a semiconductor laser element, a hologram element as a light branching element and a light detecting element are incorporated into a package (supporting member). In this configuration, a laser beam emitted from the semiconductor laser element is guided onto a surface of the optical disc which is the optical recording medium so as to be reflected, and the reflected laser beam returned from the surface of the optical disc is diffracted by the hologram element to thereby be guided to the light detecting element.
As a semiconductor laser device of this type, one disclosed in the Japanese Unexamined Patent Publication No. Hei6(1994)-5990 is known.
FIG. 7 is a schematic diagram showing the structure of another conventional semiconductor laser device of the hologram laser type than the one shown in the Japanese Unexamined Patent Publication No. Hei 6(1994)-5990 (In FIG. 7, the device is illustrated with a part fractured so as to show the inner structure). The device of this example uses a metal stem as a supporting member.
In FIG. 7, the reference numeral 71 indicates a stem as a supporting-member, 72 indicates a semiconductor laser element, 73 indicates a light detecting element for detecting signals, and 74 indicates a cap. The reference numeral 77 indicates a hologram element as a light branching element having diffraction grating patterns shown by the numerals 75 and 76.
On the top surface of the stem 71, plane areas, horizontal and vertical, are provided, on which the light detecting element 73 and the semiconductor laser element 72 are mounted. Both the left-end surface 71a and the right-end surface 71b of the stem 71 are formed as arcuate curved surfaces.
When the semiconductor laser device is incorporated into a part of the optical pickup, the left-end surface 71a and the right-end surface 71b each having the arcuate curved surface are pressed so as to be fitted into a portion being the reference (reference portion) such as a cylindrical window having an arcuate curved inner surface provided in the pickup housing, in such a manner that the both arcuate portions coincide with each other, to thereby position a vertical optical path (an optical path of a laser beam advancing in an approximately vertical upwards direction with reference to the top surface on which the elements are mounted).
Then, in the state that the semiconductor laser device is installed in the reference portion (arcuate curved inner surface), the semiconductor laser device is turned within the angular range of ±5° around the vertical optical path. With this process, three beam spots emitted from the semiconductor laser device are adjusted so as to be in the optimum arrangement on the pit row of the disc surface. This adjustment is called a turning adjustment.
It should be noted that in FIG. 7, wires for electrically connecting electrodes (terminals) of respective elements mounted on the stem 71 and leads 78 for outer connection (provided so as to be insulated from the stem 71) are not shown.